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When is pre-heating a piston engine important, and how does one pre-heat correctly?
As temperatures here in New York plunge toward (and below) freezing it's time for those of us without nice heated hangars to start thinking about pre-heating our aircraft before we turn the key.
Lycoming SI 1505 tells me that "The use of pre-heat will facilitate starting during cold weather, and is required when the engine has been allowed to drop to temperatures below +10°F/-12°C (+20°F/-6°C for –76 series engine models)", but the general recommendations I've been given are to preheat if it's been below freezing in the last 4 hours.
At what temperature does it start to become beneficial to preheat a piston aircraft engine prior to starting, and how does one ensure that the engine is thoroughly and evenly heated?
I'm pre-heating on the ramp, using a forced-hot-air heater.

I'm going to be referring to an old AvWeb article by Mike Busch with my links in this post.
As with most of what Mike writes, it's worth a good read.
Why is Pre-Heating Important?
Pre-heating your engine in the winter is important for a bunch of reasons, but there are two main ones that should get your attention - the first is preventing metal-on-metal wear by ensuring all parts have adequate clearances to function, and the second is improving lubrication by making sure your oil is ready to flow, and the spaces it's going to flow in to are opened up enough to let the oil in.
Metal-on-Metal Wear
Starting a piston engine is responsible for most of the wear the engine sees in its life - surfaces which have long since had their protective coatings of oil drip off are banging together while you crank the engine, and for a few seconds after startup until the oil pump can build up pressure and splash lubrication in the crank case can thoroughly coat the other moving parts.
In the case of a truly cold start there's an additional complication: like 2NinerRomeo points out, different metals in your engine have different coefficients of thermal expansion, and you have steel (probably several alloys), aluminum, brass, and a few others in your powerplant. When cold the clearances between these metals can be so tight that the additional wear is substantial, and at a certain point you may even damage the engine by attempting a start, shaving or spinning bearings and scuffing cylinder walls with the rapidly expanding pistons once the engine fires.
Lubrication
The other factor to consider in a cold start is lubrication - both the oil doing the lubricating, and the spaces into which it needs to flow.
Take the dipstick out of a cold engine and you will marvel at how the oil just clings there in a thick layer (this is especially true of heavy single-grade oil like 100W, but even 15W50 starts getting very sticky down in the 30°F-35°F range).  Oil that has thickened up from the cold doesn't pump very well - your engine may take a longer than normal time to develop oil pressure, and narrow spaces may get little to no lubrication until the oil has heated (and thinned) enough to get through the narrower oil galleys and tight spaces between some components.
Those tight spaces, as I mentioned under Metal-on-Metal Wear, tend to be tighter when it's cold, which means it's even harder for oil to work its way in and build up a good film of fluid. Until that film is built up and doing its job your engine is really inadequately lubricated, even if it's running. (Check out the webinar video in 2NinerRomeo's answer where Mike Busch goes into a lot of detail on how oil works, he has a nice explanation of the fluid film lubrication process.)

How do I make sure I do my preheat right?
The best preheat possible is spending the night in a nice, warm, heated hangar. It basically guarantees that every part of your aircraft has been brought up to the same temperature, and even affords you a nice place to preflight as opposed to doing it out on the ramp in the 6-but-feels-like-60 knot winter winds.
A hangar preheat isn't just the best for your engine -- your gyro instruments get brought up to a nice warm temperature (remember, mechanical gyros have to spin up, and they have the same issues as your engine did in terms of clearances being reduced by the cold), and the ship's battery gets warmed up too so it's ready to provide its best possible cranking current.
I don't have a hangar you insensitive clod!
Unfortunately some of us (like ME) don't have hangars - heated or otherwise - or our local FBO charges a hefty sum to spend the night in the warm. Those of us without hangars have to make due with a ramp pre-heat of some kind.  I'm going to assume you're in the same boat as me (no hangar, no electricity), and have to use some other technique.
Most ramp pre-heats where you have neither a hangar nor electricity take the form of a "forced hot air" system - either one wheeled around by the FBO, or portable ones powered by propane. There are even ones built around a camp stove which are deceptively good at the job (and in a pinch can burn the avgas you drained checking your tanks for water).
The general procedure for a forced-hot-air preheat is to point the heat into the cowl's cooling inlets, letting the warm air flow over and around the engine and out the cooling outlets. Start the heater up before your preflight, and with a little luck by the time you're done with the walk-around your engine will be ready to start.
If it's extremely cold you may want to block part of the inlets and put a blanket over the cowling during the pre-heat to help keep the heat trapped on the engine, and as 2NinerRomeo points out, when using a high-intensity heat source like a propane heater make sure you don't pump so much heat into the cowling that you blister your paint.  A gradual warm-up is what you want - we're slow-roasting the engine, not broiling it.
How do I know the preheat is "done"?
There are three common ways to tell if your preheat has had enough time to adequately warm your engine - each technique works pretty well, and you can use whichever makes the most sense for your situation.
Testing by feel
This is classic if you have a cowling that can be easily opened like most Piper aircraft, just feel all of your cylinders and the crankcase. They should, if your preheat was thorough enough, all be slightly warm to the touch. It's low-tech, but it works well if you can use it.
As a practical matter it's usually easier to tell if the "top end" (cylinders) are ready this way than it is the "bottom end" crank case / crankshaft / bearings), but with some cowlings (many Cessnas, or my Cherokee 180) you're simply not getting your hand in there to feel the engine: you can reach the front cylinders and a bit of the case, but the aft half of the engine is basically inaccessible without taking the cowling apart (and losing all that trapped heat).
Testing with the dipstick
Another good indicator is that when you take the dipstick out of the engine the oil flows off nicely -- compare with how thick and syrupy the oil was in the cold engine and is should be obvious when it's "ready".
This works for pretty much every engine, even if the only access you have is the little oil door, but it's also one of the slowest & most conservative indicators: pretty much all the thermal mass of the engine needs to heat up before the oil in the sump is going to get warmed up and start to loosen up.
Checking with your instruments
The final way to check the status of your preheat is to check your engine instruments: If your cylinder head temperatures are all reading something reasonable (say 60-70F) and your oil temperature is at least "off the peg" your engine has been thoroughly heated.
This technique is a little instrumentation-dependent though -- some engines may not show an oil temperature indication until you get your oil up into the 90 degree range (which would be great for start-up, but lousy for sitting on the ramp waiting). For those engines you probably want to use the dip stick test to check if the oil is "ready".
This technique also works best if you have individual cylinder probes, as you can determine if your engine has been evenly heated (this is especially true of longer engines, like a 6-cylinder powerplant: if the front cylinders have been getting blasted with warm air and are in the 90s, but the rear cylinders are still reading 30 degrees you may need to adjust your preheat procedure to warm those rear cylinders!)

Parting Thoughts - Stuff outside the engine compartment?
I've concentrated mostly on pre-heating the engine, which is what most people think about when they think about pre-heating aircraft, but as I mentioned briefly it's worth noting that other parts of the aircraft benefit from pre-heating too.
For example, a warm battery (60-70°F) will crank better than a cold one. If your battery is in the engine compartment it will get warmed up during your preheat, otherwise you should be aware that cold starting puts a pretty heavy demand on the battery, and your battery will appreciate if you limit cranking as much as practical.
Similarly, your gyro instruments (turn & bank, directional gyro, attitude indicator) will all need to spin up - that happens in a hurry (as soon as you hit the master for the electric ones, as soon as the engine catches and the vacuum pump starts really spinning for the vacuum driven ones).
If you can direct some warm air into the cabin your gyro instruments will thank you (and you'll probably thank yourself - those control yokes are COLD!). The gyros take less of a beating than your engine, and certainly cost less to replace when they wear out, but keeping them happy is worth a little effort.

If we had a blog that would definitely need to be in it. Well done.

Funny, I figured out who'd written this well before I got to the bottom :)

Another heating method is the coleman sportcat propane heater. I put it in the engine cowling the night before and the next morning it's good to go.

Well now we have a blog!!

Mike Busch, in an EAA webinar dated 8 September 2011 claims fantastic Engine longevity. He calls a start with the engine below 20°F a significant wear event, recommending preheat below 32°F.  Pumping forced air through the cowling for 15 minutes, time enough for a thorough preflight, records check etc, should do the trick.  Be careful not to blister the finish on your cowling.
Concerning the "Why", I suppose the main reason is that aluminum and steel composing the engine have dissimialr Coefficents of thermal expansion (Cte), and cold temperatures, far outside their operating range, can move the fit of parts out of tolerance.  Regarding "How" to make sure your engine is sufficiently pre-headted, I suppose you could watch the oil temperature guage.  Mine starts at 50F. I would be comfortable starting the engine if the needle had at least made it off the peg, but this may take a long time.  Since Oil plays such an important role in temperature control of the engine, some preheaters attach magnetically to the oil pan. I have heard of some pilots sending heated air up the exhaust stacks in an effort to heat the internals.  I don't know how effective that is in heating the oil.

Can you expand a bit on the "Why" and "How" aspects - especially how to tell the preheat is "done"? (I know Mike covers this in great detail in that webinar and a few others, and I think he even had an AvWeb article about it back in the day - I'm basically looking for a summarized version of that so people can read it rather than having to wade through hours of webinars like I did. If you want to write the chapter and save me the effort I'm more than happy to let you have the rep :-)

I added a few more notes. Depending on what instrumentation you have, Oil Temp, CHT etc, you could use those.  If you don't have them, you could put a thermocouple on your engine and get some representative numbers in different temperatures and find a period of time that works at those temperatures.

That's more along the lies of what I was looking for :-)
If you don't have CHT instrumentation the oil gauge is often a good proxy - so is feeling around the engine and making sure it all feels warm, then checking the dipstick to make sure the oil flows off nicely.


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What is the immediate cause of liftoff?
If I understand correctly, when a plane transitions from takeoff roll to being airborne, it is not something that happens "by itself" when the airspeed is high enough, but is caused by deliberate pilot input somehow.
Which control surfaces are involved in causing the plane to lift off?

Is it an ordinary nose-up movement of the elevators? That is, the elevators create negative lift that pushes the tailplane down, which makes the entire aircraft pivot around the main gear and increases the wings' AoA enough to create lift that takes the plane off the ground.
Or is it something that increases lift with unchanged attitude, such as a symmetric aileron movement, or an additional flaps extension? And then after the plane is airborne it is rotated to climbing attitude?

The descriptions I can easily Google up point towards 1. However, while that makes perfect sense for tricycle gear I don't see how that would work with taildraggers. Pushing down on the tail would just increase the downward force on the tail wheel rather than change the AoA.

During the takeoff roll, taildraggers will lift their tails and assume a level pitch attitude.

Various training films for WWII-era military aircraft give takeoff instructions much like the ones in https://youtu.be/XH6JMVxlf4Q?t=775 -- which is to say, the pilot does not make any deliberate input to get the wheels off the ground other than to turn the power up and to keep the plane from yawing. But those are high-performance aircraft.

The answer is indeed (a). For tailwheel aircraft, what typically happens is typically the following:

With all 3 wheels on the ground, you start gaining speed by increasing thrust.
Very soon (e.g. much sooner that the minimum take-off speed), you push the stick to lift the tailwheel off the ground and put the aircraft at more or less zero AoA.
When you reach the rotate speed, you pull to increase the AoA and to lift off (as with tricycles). The required pitch up angle is much smaller than what would be needed for the tail wheel to touch the ground again.

Alternatively, you may keep the tailwheel on the ground all the way until liftoff. Since with the tailwheel on the ground your AoA is positive, you just need to reach enough speed to generate the required lift for take-off. This may not be possible with all tailwheel aircraft or may increase take-off run length, though.

The B-17 sits on the ground in takeoff attitude. It could lift off at a safe airspeed without yoke input. OTOH, may T-draggers sit at too high of AoA and could take off prematurely. Then (a) small pitch down might dump too much lift or (b) lift is insufficient when out of ground effect. Either way one was in danger of becoming a crash test dummy.

@radarbob: good input. Feel free to edit my answer to complement it!

The tail will usually lift even with neutral stick, because the wing is aft of the main gear and the AoA corresponding to neutral stick position is lower than both AoA when sitting on the ground and lift-off AoA.

As the elevators rotate to get a negative pitch angle to the horizontal (moving the tip of the elevator upwards), a pressure difference is created causing it to produce a downwards force, and as a result the aircraft pivots around the landing gear, rotating upwards.
As it does so, the wing starts to generate more lift, as can be
seen on the graph below. The higher the angle of attack- the more
lift, since the lift coefficient becomes higher, up to where stall starts.
When the lift exceeds the weight, the aircraft will lift off.

For taildraggers, the tail is normally rotated up at a low speed while the aircraft continues to accelerate, and once a sufficient speed is reached, the tail surface is again lowered, causing the wing to increase the AoA and to lift. Footnote: If I'm not mistaken, this is more of an act to improve control and reduce drag, since at some point the aircraft will lift off on it's own with it's tail-down angle of attack.

As the elevators pitch downwards: Elevator control surfaces rather pitch upwards and that creates the downwards force which pushes the tail section down, creating the mentioned pivot. Don't they?

@Hanky웃Panky http://www.m0a.com/wordpress/wp-content/uploads/2009/09/airplane-elevators.gif

Yes that also means an elevator control surface will pitch upwards (causing the tail section to push down) in order for the aircraft nose to pitch up.

@Manfred, you should really fix the "elevators" statement since the elevator surface must move upwards to produce the downwards force (which causes the nose to go up), just as HankyPanky says and your link shows.

@mgkrebbs I will clarfy it, since I was refering to the pitch angle- http://www.rc-airplane-world.com/image-files/rotor-blade-pitch-angle.gif - and viewed from the side, the tip does, as you correct move upwards :)

@Hanky웃Panky my bad for not understanding your POV.

When you take off in a tail dragger, you let the tail rise so you’re only on the main gear as you accelerate. Then, when you want to take off, you use normal elevator movements to increase the angle of attack. Yes, the tail will fall slightly when this happens. Increased angle of attack means more lift, so you take off.
If you hypothetically held the tail wheel on the ground with the elevator, the main wheels could, for a theoretical plane, lift off with the tail wheel still on the ground. But in reality, the main wing would be eventually generating more lift than the tail and so the plane would rise into the air.

I can't answer for tail-draggers, but this is how it works for a tricycle landing gear.

Initiate takeoff roll - power is applied
$V_1$ - At this point, the pilot must proceed with takeoff, even in event of an engine failure.
$V_R$ (Rotate) - at this point, the pilot pulls back on the stick, causing the aircraft to pitch up, rotating on the main gear.
$V_2$ - Rotate at this speed in event of an engine failure.

Also, if you keep accelerating down the runway, at some point you will have so much lift that the plane will take itself off.

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What's the inspection/repair procedure following damage from severe hail?
Delta 1889 was forced to make an emergency landing last Friday (August 7th, 2015) after being battered by hail in a severe thunderstorm.
The picture in the news shows the two leading segments of the windshield have been ruined and will need to be replaced.  The nose cone of the jet has been caved in.  Zooming in suggests that the sheet metal ruptured where it made contact with whatever it behind it.  If that's the case I'm assuming it's too damaged to just have the dents pulled out and will also need to be replaced.
Beyond the obvious damage, what else will need to be looked at before the plane is able to resume normal operations?

Contrary to some of the media reports that I've seen, the nose isn't made out of metal, sheet or otherwise. The piece that you see that was completely obliterated is the radome which covers the on-board weather radar. It's made out of rather soft material (fiberglass or similar) so that it won't absorb, reflect, or otherwise attenuate the signal from the weather radar. A Delta 747 also had its radome beat up by hail a couple of months ago.

Note that that  damaged Delta 747 was moved into retirement 2 years early rather than trying to repair the damage.

It's impossible to say without a lot more detail.  The damage looks superficial but as Johnny points out, a 747 was retired with damage that looks from the photo, even more superficial.

@Simon In an airplane, just because it's superficial doesn't mean it's cheap. :( Even in a small turboprop, the windshield and radome can be hundreds of thousands of dollars.

@Johnny Did they confirm that they're retiring it? I saw where they had moved it to the boneyard, but wasn't sure if they were sending it there for repair or retirement (planes are also repaired there frequently.)

@reirab  Oh, I know that.  You are talking to someone who instead of pulling the door unlock handle pulled the emergency blown down handle on the cockpit door of a Vulcan, enabling 2500 psi to hammer the door into the towing arm.

@Simon I'm not sure I agree about the 747's damage being more superficial.  It's windshield was intact; but it took dents all over the wings leading edge which this a320 appears to have avoided.

They would have to work from the nose back to ensure there was no other damage but the first thing they would look at is the nose its self. As mentioned that cone is not metal as it houses the aircrafts weather radar behind it. Specifically a Honeywell unit like this one. By the looks of it the element was damaged and most likely needs replacing. From there you would come to the forward pressure bulkhead which, considering the damage would need to be closely inspected. Here is a pic of one from a Boeing for reference.

Degraded or improperly fixed bulkheads have lead to issues in the past. While this is happening they will also work on the windshield and check the struts around it for damage. They would also look over all forward facing surfaces, just a guess but they would check the wings leading edges for damage, engines, leading edges of the horizontal and vertical stabilizer as well as whole airframe for possible damage along its axis'. The question of will the plane ever fly again is more a question of cost than mechanical issues. For what its worth just about anything can be fixed, if and airline will fix it mainly depends on if its cheaper to fix or simply buy a new plane.

All forward-facing parts need to be inspected and replaced if they show signs of damage. This includes:

The radome, obviously, the surrounding structure and the weather radar below it.
The windshields and the surrounding structure.
All leading edges and the high-lift devices attached to them. This includes all tail surfaces.
The fan blades of the engines, the cowl lips and the central cone. Even though the engines look undamaged superficially, I would suspect that the fan blades have suffered multiple impacts and have developed cracks as a consequence.
All instrumentation, antennas and probes which are not flush with the airframe.

To get an aircraft certified for scheduled service after this kind of damage will take several weeks if done properly. It may be flown after a thorough check and quick fixes, not for passenger service, but to transfer it to a better location to repair the damage. You probably wouldn't believe what can be made flightworthy again with the right sort of sticky tape.

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What procedures exist to take control from an "unsafe" pilot?
I was reading up on the Garuda Indonesia Flight 200 crash and a few questions came to mind, in summary the captain (PF), conducted an unsafe approach in which he did not heed multiple warnings from both the aircraft and the copilot (PM), and landed 860m past the threshold and at a speed of 221kts.
The wiki article also states: "The copilot failed to take control of the aircraft ...  as required by airline policy". This just got me wondering, what policy/procedures exist in outlining how to take control of an aircraft from an "unsafe" pilot. I know the procedure under normal circumstances is "my aircraft/your aircraft". But how would this be accomplished in a situation similar to Flight 200, where it seems the captain would have of been reluctant to hand over controls given his blatant disregard for all other safety measures.

For completeness, that was PK-GZC, a Boeing 737-400.

Related (maybe a dupe?); also related

Unless you have a copy of that airline's SOP, this may not be answerable. as required by airline policy  I'll recommend that you look up the search term "cockpit gradient" or "authority gradient" to get a feel for this non trivial CRM challenge.

As Korvin says, that's going to be hard to answer because it will vary by airline and boils down to the individual FO. (In the opposite situation where the captain is PM there wouldn't be any hesitation) I suppose if the FO felt his life was in jeopardy then policy and procedures might go out the window anyway. That said, most major airlines will have a set of parameters that define a "stable approach." Outside those parameters the FO will have authority to call it off. What happens if the captain refuses to cede control is the kind of pickle you probably can't make policies for.

@TomMcW Last sentence of your comment nails it. :)  Well said.

This is a true "nightmare scenario" and really approaching -- if not beyond -- the limits of the realm of CRM.  The assumption of CRM is that while pilots can get task saturated, focused on "making it (the approach) work out", and otherwise lose track of the situation, everybody is willing to listen to reason, if it is just presented with sufficient clarity.  If a pilot is so far gone beyond that point that he is absolutely determined to take his approach to its completion, you're approaching a different scenario.
Let's stipulate at the outset that this sort of a scenario is incredibly rare. Good pilots can get so focused on making things work that they lose situational awareness, but a clear statement like "we're 40 knots fast & two dots high on glide slope, GO AROUND" will typically snap pretty much everybody out of it.  The captain who is so wrapped up in his authority that he's willing to ignore an FO's repeated direction to go around is pretty rare.
That said... in the nightmare scenario, the FO's options become:

Keep making callouts, more directive, more urgency, yell louder.
Tell ATC that "we need to go around" on the hope that ATC directing "Flight 123, go around, fly runway heading, maintain 3000 feet" may accomplish what the callouts didn't.
Raise the landing gear.
Push the power up or otherwise fight for control of the aircraft.
Attack the flying pilot, perhaps with the aircraft logbook (metal cover) or a heavy flashlight or some other improvised weapon.

At this point, the FO is in the awful spot of having options that have a limited chance of success and in several cases, huge risk of making a bad situation even worse.  There is no "policy" solution to this sort of a scenario.  That a captain would have ignored repeated GPWS callouts and FO callouts is beyond the realm of what policy ever imagines.
As I said before, this sort of scenario is almost unimaginably rare.  Pilots just don't often reach the level of being an airline captain without sorting out the need to accept a "Go Around" callout from their First Officer.  Are there arrogant pilots out there?  Absolutely.  Arrogant enough to get to the situation mentioned in the OP?  Very, very, very few, and very far between.

Fortunately, they are " Very, very, very few, and very far between." or aviation wouldn't be as safe as it is.

and yet it happens.


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Safest place to seat oversize and/or limited mobility passengers on a passenger jet?
From the simple perspective of how to save the maximum number of lives, where is the best place to seat oversize passengers and those with limited mobility?
I was in the over-wing exit row on a recent flight and noticed that exit appeared to smaller than the main doors. Also the exit row is reserved for fit and mobile passengers.
Do emergency evacuation strategies take this into account - is it best to seat the old/infirm/oversized passengers at the front by a full-sized exit - where they can be assisted out ASAP in an emergency? Or is there are risk of a log-jam of limited mobility people blocking a hoard of able bodied passengers behind them? Or maybe the ideal solution is let the able-bodied swarm out immediately, and then let the remaining exit in their own time?
Ocean liners have a tradition of following the 'Birkenhead rules' (aka 'women and children first' - unless it's an Italian ship of course!) but they have the luxury of a bit more time and space control the evacuation.
Or maybe aircraft crashes are just so chaotic there's no point in trying to plan anything?

There is no safest place in an aircraft. But logically being not too far from an exit can help one with reduced mobility, specially close to an "able-bodied passenger" assigned by the attendant to open the exit if required and the attendant is not available.
Flight attendant manuals can include such instructions:

Before each take-off and landing you should prepare yourself for a possible emergency by using the 30-seconds review. Consider such things as:

The location of possible ABP (able-bodied passengers) with particular attention to military and airline personnel who can assist you;
The location of those passengers who will need special assistance (physically challenged, unaccompanied minors, pregnant women, elderly etc)

(Defunct Freedom Air FAM)
ABP will help if needed and instructed by attendants. Such guidance implements the recommendation in IATA in Cabin Operations Safety best practices guide:

Below is a mnemonic for Silent Review used by some operators to help review some critical components. This example is known as “OLD ABC”:

O – Operation of exits
L – Location of emergency equipment
D – Drills (e.g., brace for impact)
A – Able-bodied passengers and passengers with reduced mobility
B – Brace position
C – Commands

IATA is the syndicate of air carriers. Transport Canada template of Flight Attendant Manual.
Flight attendants are trusted crew members, highly trained for passengers safety, this is their first task, well before welcoming passengers and selling drinks.

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What are the benefits of using spoilers/airbrakes for lateral control as opposed to ailerons on the Rockwell B-1b?
The Rockwell B-1b uses pairs of airbrakes/spoilers on each wing in replacement of ailerons for the lateral control of the aircraft. Was there a particular advantage to this because of its variable swept wings or because of its mission role being a high altitude supersonic bomber?

Doing away with ailerons helps to reduce the wing area by allowing to extend flaps over the full span. This is not unique to the B-1, other swing wing airplanes (F-111, Su-24, MRCA Tornado) also use spoilers together with differential deflection of the horizontal tail surfaces for roll control. With full-span flaps, the desired minimum speed can be achieved with a smaller wing area as opposed to the partial-span flaps of a wing with ailerons.
Another reason is to reduce wing loads. The B-52 is rolled by using spoilers, not ailerons, in order to reduce wing torsion and extend the structural life of the wings.
With fly-by-wire systems that allow to vary control deflections and functions depending on speed and angle of attack, roll control by differential tail deflection has become ubiquitous, even on airplanes with conventional ailerons.
To my knowledge, the first design which extended trailing edge flaps over the full span and relied on spoilers for roll control was the Messerschmitt M37 (early version of the Bf-108) which was designed to compete in the FAI Challenge International de Tourisme 1934.

Never mind, maybe already asked.

My first, (and seemingly most obvious...) impression would be to reduce or eliminate adverse yaw caused by induced drag out at the end of the upgoing wing when you don't have a tail surface to counter it.  Is this not a concern?

@MichaelHall Yes, this is also a concern. If you have the massive vertical of a B-52, however, maybe less so. The B-2 opens its split ailerons halfway so it can reduce drag one one and increase it on the other side when rolling.

Thanks Peter.  Is it enough concern to include in your answer?  ;)


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What system is there in the UK to prevent collisions between small aircraft?
I met someone the other day who owns a small plane and he was going to fly from Cambridge to the Isle of Wight.  I asked him whether he had to file a flight plan and he said no.
Just wondering therefore how such collisions are prevented?

Most air collisions in the uk seem to between military aircraft.

@RedGrittyBrick formation flying is always dangerous, and a lot of the accidents involved trainer aircraft, so probably were formation flying training...

Small airplanes will be under VFR (Visual Flight Rules) which entails that the pilot looks out the window and is responsible for staying away from other aircraft and staying out of the clouds (the fog banks of the sky).
If you see another plane in your path then there are standard rules to avoid him see this question.
They can fly under IFR (Instrument Flight Rules) but that requires that Air traffic control monitors the airplane and steers it away from other planes.

thanks.  I'm quite surprised that it relies on pilots being vigilant... for example what if one plane is descending and another climbing... it's got to be difficult always to keep a visual watch in 3 dimensions... presumably there haven't been many collisions otherwise this system would have been called into question...

@mikerodent The pilot must always be vigilant

@mikerodent There are quite a number of accidents and incidents involving small airplanes. Not only mid air collision but also cases of small aircraft straying unintentionally into controlled airspace. There is work going on to make it cost effective to equip small aircraft with ADS-B OUT and ADS-B IN so that an extra early warning for nearby traffic is possible.

@mikerodent Also bear in mind that there are very few planes in the air and, also, that it's much harder to hit something in three dimensions than it is in two. For example, if you were to drive from Oxford to Dover while your friend was driving from Cambridge to the Isle of Wight, your paths would certainly cross (ignoring the possibility of bridges) and you would crash if you both reached the crossing point at the same time. However, if you both flew, your tracks over the ground would have to cross but you might fly over that point at different altitudes as well as at different times.

@DavidRicherby yes, that thought had occurred to me... and ultimately engineers deal in probabilities (e.g. that a wing won't fall off an A380)... but the VFR system described is, it seems to me, clearly sensitive/vulnerable to the number of people owning and using small aircraft, and to the restriction of usable areas if ever controlled areas are extended.  Particularly in proximity to the runways where small aircraft take off and land.

@mikerodent Do read the linked post.  There are some rules of thumb which a well trained and clear thinking pilot will use which greatly reduce the risk of collision.

@Simon I shall!  Just another thought about DavidRicherby's comment about 3 dimensions making it harder to hit: of course a "prang" between two cars will be fatal only in a tiny fraction of cases... in the case of air collisions 99% of the time all airborne people will die and in a densely populated country like the UK chances must be non-negligible that there will be victims on the ground as well: i.e. gravity is an unforgiving force.

@mikerodent you are welcome to the chatroom and discuss the dangers of flying. (comments aren't the place for extended discussion)

@ratchetfreak Sorry! you're right of course, my bad.

@DeltaLima: I though the main problem with transponder/ADS-B on small planes is power. It has to have certain range and therefore needs certain power which simply isn't available in gliders and ultralights.

@JanHudec One of the things that is being looked at is to reduce the transmission power of the ADS-B transmitter. The peak transmission power is still quite high, but due to the few and short transmission, the total power consumption can be quite low. A battery powered solution operating for several hours is feasible. In fact, quite a number of gliders and ultralights are already equipped with ADS-B with today's higher power requirements

Thats a really insightful point Mike about being extra careful around airports and other areas where small aircraft collect such as the low level corridor between Manchester and Liverpool. I am sure that many pilots feel like I do that making more controlled airspace is not automatically a good thing if it forces other aircraft into ever smaller places.

Glider student here.
There is no electronic or administrative system which can replace pilot vigilance.  In the US (I am not familiar with the regulations anywhere else), the end responsibility to avoid other aircraft ALWAYS falls with the pilot in command, even when given clearance/directions from ATC.
There are systems to help though.  Popular with glider pilots (especially in Europe, but increasingly in the US) there is a system called FLARM which broadcasts GPS and baromatric data.  Other aircraft with FLARM units within range receive this signal and selectively warn the pilot of collision hazards.  FLARM has a number of shortcomings which pilots must be mindful of; eg: aircraft without a FLARM unit are not tracked, it has limited range so it isn't very helpful for distant or fast-moving aircraft.

According to Wikipedia: "In the UK the telecom authority and Civil Aviation Authority confirmed in 2007 that FLARM was acceptable and so it is also being adopted there."

Under Visual Flight Rules (VFR) "See and Avoid" is used. For every 9 seconds spent looking out of the cockpit scanning the sky for other aircraft, the pilot spends 1 second inside the cockpit checking instruments etc.
An important part of this though is that if the aircraft is equipped with radio then the pilot should talk to an air traffic service, even a procedural service like London Information is useful, because a) the information service will tell the pilot of other known movements in his area and b) by giving out PACER (position, altitude, conditions, estimate request) reports, other VFR aircraft will be able to listen and if necessary change their own altitude in advance if there is any doubt about seeing the other aircraft in time.
Not all VFR aircraft have radios though. There are additional rules like not flying too close to clouds. I believe one reason is that you don't want another aircraft to appear out of a cloud just feet away. Ultimately though, its the MK1 eyeball and the owner of that eyeballs responsibility not to run into other aircraft.

+1 the importance of radio communications for seeing other aircraft in time.

Yes its not really see and avoid, its listen and avoid, as in, listen and if you can't see an aircraft that is in roughly your location, make sure you are at least 500 feet above or below their reported altitude. This also gives you a direction to look in - up or down.

Whilst there isn't really a good all round on board system for GA aircraft in the uk. It's good practice to get a Lower Airspace Radar Service from a nearby unit if available.
The level of service depends on how busy the unit is, but generally you can get some form of deconfliction service which provides traffic information and avoidance steers.

To add - you don't need to be IFR to get a LARS service.

As has already been mentioned, the primary method of avoiding other aircraft when flying VFR is to simply look out the window and don't fly into another aircraft. However, pilots in the same area are also usually in contact with each other by radio on a frequency that is determined by where the aircraft are operating. Pilots advise each other of their intentions by radio, which allows other pilots to know where they are and what they're planning to do.
The specific case of around airports was mentioned in a comment earlier. This is indeed the area where pilots have to be most vigilant in avoiding other traffic (because there's more of it around airports.) However, for uncontrolled airfields, there are specific, standard traffic patterns that pilots are supposed to fly when approaching or departing from a given runway. While pilots should always be vigilant in monitoring every direction, following this pattern allows pilots to know where to expect other aircraft to be around the airport and monitor those areas most closely. And, again, pilots approaching or departing from an airfield should advise other nearby pilots of their intentions via radio.
Of course, at controlled airfields, pilots are required to maintain radio contact with the controllers and follow their instructions so long as it's safe to do so.

I am also a glider pilot. The Soaring Society of America (SSA) recently published a rather lengthy letter on collision avoidance, particularly concerning gliders and powered aircraft, in response to the FAA Advance Notice of Proposed Rulemaking.
First and foremost, midair collisions in general are unlikely, due to the vast amount of space available to maneuver vs the relatively small size of (even large) aircraft.  That being said, due to conventions and limitations near airports and air routes, along with the sheer number of aircraft, collision avoidance does become an important concern.
For gliders, collision avoidance is particularly important because they tend to be restricted in geographic range due to atmospheric or geographic features. The SSA letter particularly references how this is an issue around the space between Las Vegas and Minden, due to the ridge and wave lift available in that area. I have similar experience flying in the ridge due east of the Washington, DC metropolitan area, which also has a heavy amount of commercial jet traffic inbound to the region's three major airports.
Here are some snippets from the SSA's letter which I believe are relevant:

SSA agrees that expanded use of available forms of anti-collision
  technology in flying machines of all types – not just in gliders –
  obviously would make flying safer.  Thus, a large number of US glider
  pilots have voluntarily added to their cockpits either transponders
  (which broadcast the position of a glider to ATC and TCAS equipped
  traffic) or an alternative, effective, lower-cost technology called
  FLARM (which, in addition to broadcasting location information, also
  provides collision alert data in the cockpit of gliders, much as TCAS
  does in the cockpit of larger, more expensive aircraft.) FLARM has
  been widely accepted worldwide and has the support of the European
  Aviation Safety Agency (EASA.)  It is so successful and effective that
  the use of FLARM (rather than transponders) is now mandated for
  gliders flying in French airspace.

According to SSA's research, FLARM is more effective than transponders, because transponders require active involvement from the FAA controllers, and controllers typically clear VFR aircraft (which includes gliders) from their screens.

Transponders are not true collision avoidance devices in that they do
  not provide any direct information to the pilot.  They may be useful
  to other pilots who are equipped with a TCAS (or similar) device, but
  because of very high costs those devices are not in widespread use
  except by the highest end of the aviation community.  As an additional
  issue, when air traffic controllers have too many targets on their
  displays, they may suppress VFR traffic, which would include
  transponder equipped gliders.  And as a matter of policy, ATC does not
  necessarily give IFR traffic advisories on uncontrolled VFR traffic in
  its vicinity even if that traffic is transponder equipped.  (Gliders
  rarely operate under positive ATC control and are therefore generally
  “uncontrolled” even when operating a transponder).  Aircraft that fly
  VFR only and are not in contact with ATC derive essentially no direct
  safety benefit from equipping with a transponder; doing so only
  assists ATC in applicable areas and the high end users of the NAS that
  are equipped with expensive collision avoidance devices like TCAS; or
  in the case of gliders, with PowerFlarm.

...

Each FLARM device determines its position and altitude with a highly
  sensitive state of the art GPS receiver. Based on speed, acceleration,
  heading, track, turn radius, wind, altitude, vertical speed,
  configured aircraft type, and other parameters, a very precise
  projected flight path can be calculated. The flight path is encoded
  and sent over an encrypted radio channel to all nearby aircraft at
  least once per second.
At the same time, the FLARM device receives the same encoded flight
  path from all surrounding aircraft. Using a combination of own and
  received flight paths, an intelligent motion prediction algorithm
  calculates a collision risk for each received aircraft based on an
  integrated risk model. The FLARM device communicates this, together
  with the direction and altitude difference to the intruding aircraft,
  to the connected FLARM display. The pilots are then given visual and
  aural warnings and can take resolutive action.

Read more from the SSA Letter http://www.ssa.org/GeneralNews?show=blog&id=4035


text:
Why do we call moving an aircraft on the ground "taxi"?
We all know what "taxi" means to general public -- a car which carries you from A to B in exchange for your paying a fare.
"Taxi" also means to drive an aircraft on the ground. Why do we call it that? What's the reason & history behind the term?

You might get an answer on english.SE if no one here knows; they have a lot of etymology questions

According to the OED, the word "taxi" derives from the word "taximeter," used in 1894 in The Times, which in turn is from "Taxameter-Fabrik" used in an 1890 German patent for a device to record distance driven for use by hire vehicles transporting passengers (relatively) short distances from point to point. (Wikipedia has a more detailed etymology.) Cabs (from "cabriolet") using this device were originally referred to in English as "taximeter cabs," which was soon enough shortened to "taxi-cab" and even "taxi."
Over the next few decades usage of the word "taxi" was expanded to encompass a great number of other meanings, mostly consistent with the idea of a "short trip" or "short-term hire" (e.g., "taxi dancer").
"Taxi" in the sense of "to travel slowly along the ground or water under the aircraft's own power" seems to have come into use around 1911-1915 in aircraft industry-specific publications. Without being able to talk to the writers who coined it it's not possible to definitively say why they chose this term, but it seems likely that it came from the various uses of "taxi" in the sense of a "short trip."

This online etymological site suggests that an airplane moves slowly across the field in a similar fashion to how a taxi-cab driver would slowly make his way down a block looking for fares, and the term is borrowed from that behavior.

The link to Dictionary.com also describes the use of taxi as "Shuttling back and forth between two points" - just like you would between runway and stand.

I'll throw a thought in the mix although the term most likely pre-dates this: When you are running a plane on the tarmac the "meter" is literally running since the engines are on. Much like the meter that starts running when you get in a taxi cab. There is no worse feeling than renting a plane for a nice day of flying and getting stuck in a departure line watching the Hobbs slowly tick on while you sit there hopelessly.
Interestingly the history of the word "taxi" as we use it for cars dates from the word taximeter the device installed in taxicabs to measure fare. Which comes from the french taxer-mètre. The evolution may come from the fact that the ground operations of the aircraft are part of the ticket which you paid for.
(Its a long shot but its worth a thought)

Although I don't think this is the answer, I up-voted it anyway cuz I can just imagine how that feels!

Horray for fields with low traffic volume. :) I don't think I've ever had more than 1 airplane in front of me for takeoff at the field I'm normally flying from.

This seems to be purely speculative.

This is purely speculative but anyone who has ever rented a plane knows this feeling, and its terrible. Taxing has been going on far longer than hobbs meters have been measuring engine time.


text:
What is the chord of a wing?
In the answer to this question the author mentions the chord of a wing.  What exactly is that, and how is it used in wing design?

the Chord is the line stretching from the leading edge of the wing to the trailing edge parallel to the centerline.

There are different variations to describe the chord of the whole wing.

The Standard Mean Chord
Defined as $\frac S b$ with $S$ the surface area and $b$ the span of the wing. This is not used in aerodynamics.
The Mean Aerodynamic Chord
Defined as $\frac2 S \int_0^{\frac b 2} c(y)^2 dy$ with $y$ the coordinate along the wing and $c(y)$ the chord at $y$.
For swept or delta wings this gives the equivalent chord for a rectangular wing, and is important for placing the Center of Gravity for stability.

Could you comment on how the chord is considered when creating a wing?  Perhaps how it effects lift and stability?

In most caes, the chord is simply the size of the wing in streamwise direction. As this varies over span, there  are different ways of computing the average, but for the answer on the X-1 control issue, those differences are academic. If you increase the chord, lift goes up almost linearly and stability decreases, because now the wing's lift force has a longer lever arm in flow direction. By increasing chord, you decrease aspect ratio, but the effect of this is better explained in a full answer to a new question.

@PeterKämpf I'll be honest, I'm not sure how to even ask that question.  Starting to think I just need to pick up a book on aerodynamics and wing design (for dummies, in my case.)

@Jay Carr: Yes, that could be a start, but doesn't give you the interactivity you find here. If you think you could annoy the others - if they answer, they clearly are not annoyed.

@PeterKämpf You should come into the chat at some point, so I can ask you a few questions about it then ;)

@Jay Carr: I rather prefer to use graphics and formulate my answer carefully. Come on, give yourself a push and post that question.

@PeterKämpf Okay okay fine: http://aviation.stackexchange.com/questions/5047/how-does-chord-length-affect-wing-design  I think I got it out in that question...


text:
Why don't pilots parachute from small planes that are in distress?
There was another question that asked why commercial flights don't have parachutes.  The almost ubiquitous response was that the parachutes would be useless because:

Most accidents with commercial airliners happen on take off and landing, and there is no time to parachute.
In order to get to a position where 100+ people can successfully jump out, you'd most likely need to descend some 20,000 ft and then maintain straight and level for a good 3 to 5 minutes once you got past 12,000 (so people have oxygen to breathe when they jump).  And if you can descend and maintain level flight, you might as well land.

But what about in a light, single engine plane (think Cessna 172 or Piper Cherokee)?  Engine failures in small aircraft, for example, seem to be more common, so you have more accidents that start high above the ground.  Thus, you usually have a few minutes before you're going to hit the ground and there's often only 1 or 2 passengers (rather than 100). Plus, you're usually already at an altitude where you don't need oxygen to bail out.
With that in mind, couldn't you put the plane into a shallow dive to keep it from stalling, trim it to keep it going straight and then bail out?  It seems like a somewhat practical solution, yet I have never heard of anyone doing it.
Why do pilots often try to find a road to land on or a lake to ditch in when trouble strikes instead of just bringing a parachute and bailing out?

It might be noteworthy that just about all glider and a lot of motor glider pilots wear chutes. There have been number of successful emegency exits, and in case of gliding some developments to facilitate exits, like the Roeger-Hook or (more exotic) DG´s NOAH-System.

@yankeekilo I flew gliders for a few years and never saw anybody wearing a parachute unless they were doing aerobatics...

@Lnafziger this is interesting - at least in several European countries (e.g. Germany, France, Switzerland, Austria, Italy, Spain) I have not yet seen anyone without parachute. For competitions those are mandatory (not sure if that is international, too).

Gliders are a bit of a special case. Sport gliders often fly in close proximity, and so have a higher-than-average chance of mid-air collision. They are also easier to exit from.

@yankeekilo I never got involved with competitions, but I vaguely remember them being required in that situation here in the US as well.

When I went on an Intro to Gliders flight, we were required to wear parachutes.  Also required when flying aerobatics.   (I'm looking for precise citations)

I'm not even sure how feasible in-flight egress would be in many GA aircraft, including the C172 and Cherokee. I was in a C152 Aerobat once that had pull rings for the doors, but that was designed for use with parachutes. Could you get the doors open on a C172 with flying airspeed?

Actually, in European gliders (at least the ones I know, from 40 year old Soviet Block gliders to modern German ones) you can't even sit comfortably without a parachute: the seat is designed in a way that the parachute is your backrest.

Not that the chute would do you much good in most cases, as without proper training you're going to end up with serious injuries or worse trying to use one, and parachute training is not required (or wasn't when I got a ride in a gliders years ago), nor is proper chute selection for the size and weight class of the person wearing it.

@jwenting:  Here's a recent local instance in which a glider pilot used a parachute after his plane broke apart in midair: http://flightclub.jalopnik.com/man-bails-out-of-broken-glider-parachutes-to-a-hospita-1695949116

@FredLarson I'm not very familiar with the C172, but it's pretty easy to open the door of a Cherokee in mid-flight. My instructor has done that a few times just to demonstrate how the plane feels with the door open. You can even make (right) turns using it as a control surface. :)

Wearing a parachute is uncomfortable and would be pointless for 99.9% of all flights.  Not wearing a parachute would necessitate having to put it on before you exit; but the cockpits are cramped, and putting on a bulky parachute (while still flying a failing plane) would be impossible.

@jamesqf not saying it's impossible, but it's not very bloody likely that an person without training to use a parachute will make it down in one piece.

@jwenting: Don't know how likely it is, but per the link, it has happened.  The few times I've flown high-performance sailplanes where a parachute is required, there was no instruction other than "this is the ripcord".

@jwenting: You seem to be thinking of ejection seats, which are as potentially-lethal as you describe.

@Sean many inexperienced people end up with broken bones and worse when attempting a parachute jump.

Gliders are at higher risk of mid-air collisions due to frequent intentional close proximity when thermaling, so a parachute is far more likely to be useful.

@jwenting Broken bones are among the less serious outcomes of airplane crashes, so these are not the right criteria of comparison (I am assuming you are not using "and worse" to sneak in a reference to fatalities without making a disputable claim about the fatal accident rate.) The issue could be decided by the ratio of fatal/all attempts to bail out of gliders. I don't know where to find these figures, but I know of several successful bail-outs, and the only fatal ones I know of were at too low an altitude, in a situation where the crash would have been fatal anyway.

In the "old days" pilots did exactly what the original question proposed.  I recall reading that Charles Lindbergh made several parachute jumps while flying the mail in the mid 1920's.  Engine failure at night over an overcast or losing control of the aircraft in cloud were some of the reasons, as I recall.

Mainly because in the situation that you describe, the airplane is perfectly capable of flying.  You don't need an engine to fly as airplanes are designed to glide without it. Part of every pilot's training is how to land the airplane when this happens.
Many of the same issues also apply in the smaller airplanes.  Unless the pilot and the passengers fly around with their parachutes on, it would be quite difficult to put them on in the confined space, in a high stress situation, and with the very limited time available.  Even if they did, untrained people are going to be hurt (probably quite badly) during the landing even if everything else with the jump goes well. (See my answer on your linked question for some of the things that can go wrong during the jump.)
You are also creating a hazard with the aircraft not being piloted and crashing into a random place on the ground.  All of this when the airplane could have just glided in for a landing in a field or on a road.  Most of these types of emergencies end quite well, and even a lot of the accidents will have fewer injuries and deaths than if people were jumping out all of the time. As an added bonus, the airplane can even be used again!
On the other hand, a major structural failure that makes the aircraft incapable of flight could be a reason to jump.  This is extremely rare however, and even if one has a parachute in this situation it may be impossible to exit the airplane safely because of high G forces and the possibility of hitting the airplane as you are both tumbling through the sky.
Some manufacturers are now building ballistic parachutes into the airplane which can bring the entire airplane down safely in these situations.  This is much safer, reliable, and does have a positive impact on safety in these extremely bad situations. For just an engine failure though, I doubt that most pilots would even fire the ballistic parachute if there were suitable landing spots within gliding distance.
My view is that you would have a far greater safety impact by requiring everybody in a moving car to wear a helmet.  Would it improve safety? Absolutely. Would people want to do it? A few would (and perhaps a few do), but the general population doesn't want to be inconvenienced by something that is only a remote possibility.  The odds of a parachute helping you in a typical GA airplane is far more remote than the odds of the helmet helping you in a car.

Sincere thanks for pointing out that engines are strictly optional. This fact has not yet sufficiently entered the public domain :D

Excellent answer, thank you :).

There was an instance of the use of a plane parachute in the UK last year - http://www.bbc.co.uk/news/uk-england-gloucestershire-22798139 for more info - as it occurred over suburbs, I suspect there would have been significant damage without it.

to add to this in Finland a parachutist plane went down and only 3 people got out

This answer seems to fly in the face of the fact that apparently, many aerobatic and glider pilots do wear parachutes in the cockpit. I would suggest expanding your answer to include this fact, and either why these exceptions are reasonable or why these pilots are misjudging risk

@raptortech97 Well, two things make it very different for an aerobatic pilot (which the question was not about so I did not address it): 1) They do indeed fly around with the parachute on (which the typical GA pilot doesn't do), and 2) structural failure is more likely because of the high G-forces involved in aerobatic flight.

Ah, sorry, I misread the question

About halfway through you mention the "extremely rare" situation, in which there is severe structural damage. If it is impossible to exit the airplane safely... do you just... die?

@jaska In some cases, yes. I'm referring to instances like mid air collisions that break off a major component of the aircraft needed for flight (wing, tail, etc.). Fortunately, as I mentioned, this is extremely rare.

@raptortech97 Aerobatic pilots are at much higher risk than pilots in normal flight. I think Lnafziger's analogy of wearing helmets in cars is actually very apt. Going along with that analogy, racecar drivers do wear helmets (and have lots of other extra safety systems) for precisely the reason that aerobatic pilots wear chutes: they're much more likely to be involved in a bad accident.

"Untrained people are going to be hurt (probably quite badly)" This is a common sentiment and has even caused pilots to risk a crash-landing instead of bailing out, but where is the evidence for it? Typical emergency parachute descent rates are equivalent to free falling from a height of less than 4ft.

I compete in aerobatics where parachutes are required by the rules.
My personal criteria for bailing out are

Structural failure (a wing breaks off -- unlikely, as my main spar is enormous)
Control failure (flutter, stuck elevator)
Inability to see or control the aircraft (oil on the windscreen, maybe a bird strike)

I might jump for an engine fire just because the main fuel tank is way too close to me.
If the engine fails I would land the plane.
As noted in Lnafziger's excellent answer, an engine is required for continued flight, but isn't truly necessary for landing :-)
I compare wearing a parachute to wearing a helmet in a car.  In unusual / high performance situations, it's a very good idea.
It's unnecessary for the morning commute.
I don't wear one when flying a non-aerobatic airplane.

Something that isn't clear to me from anything on this page: assuming you are wearing a parachute already, and the plane isn't pulling any significant gees, how easy would it be to open the door and jump out?

@raptortech97: I think aerobatic planes have provision for in-flight egress. For example, I was in a C152 Aerobat once and noticed that it had a D-ring that would pull the door hinge pins. Regular C152s I've flown don't have that.

@raptortech97 It truly "depends on the airplane". Some would be quite easy,  others not so much, and others are even impossible to open in flight.

"As my main spar is enormous".  Congrats to either you or your plane... or both.  :-)

On your comment of:

Can you possibly think of an instance where having a chute would help in a GA plane?

Yes, I can, and here's a video:

Bet those guys were happy to be wearing chutes alright!

Yeah....  And that they were already outside of the airplane when it happened.   Wow, not good.  Any idea if the pilots were able to get out?

As I recall everyone got out of that one.  Very very lucky.  All trained jumpers, all wearing chutes already.

@Lnafziger - yes. One plane actually landed heavily damaged (pilot survived). The other was a total loss (obviously), but the pilot was also wearing a chute and survived by jumping

@Lnafziger I believe everyone survived from both planes. You can see one of the planes falling in a fireball if you look closely.

You don't have to look too closely to see that!

@Lnafziger Ah ok, I haven't watched it recently ;)

The video description says: All 9 skydiver landed safely, as well as the two pilots, one of which was taken to the hospital to treat minor cuts.

Sometimes pilots do wear parachutes.
It is a requirement for aerobatic flight that all occupants wear emergency parachutes.  Aerobatic aircraft are also designed for quick egress with jettisonable canopies or enclosures and quick release restraints for the flight crew.  The seats in the aircraft are also designed to accommodate an emergency parachute which doubles as a backrest or seat cushion.
The major reason for this here is the real possibility for an aircraft to depart from controlled flight or have the flight envelope exceeded, making a successful emergency or off field landing practically impossible.
In general for normal or utility category operations in a single engine airplane, nearly all emergencies will not result in a departure from controlled flight, if the aircraft is operated within the approved flight envelope specified by the manufacturer in the airplane's type certificate, airplane flight manual and cockpit placards as well as proper flight planning, weather briefing and preflight inspection.  The aircraft can also be maneuvered to and landed off field, many times with a minimum of risk.
Naturally there are some exceptions to this.  Engine failure at night and/or over rough or mountainous terrain, in IMC, or ditching in open seas can make a forced landing very hazardous.  In these situations your chances of survival may be more favorable if you bailed out of the airplane at a sufficient altitude as opposed to attempting a forced landing.
As a Cirrus pilot myself with flight time in SR20 and SR22 aircraft, I am a big proponent of the Cirrus Airframe Parachute System System (CAPS), particularly in the employment of the CAPS in the situations described above simply because the chances of survival are dramatically better than without, if the CAPS is employed correctly.
Moving into larger, multi engine aircraft the extra redundancy offered by two or more engines largely negates the shortcomings of singles in these situations and the benefits of emergency parachutes or airframe chutes.

It is common procedure to skydive from airplanes in distress, if the plane is already on it's way to altitude, carrying skydivers. There are parameters to consider though. When you are a trained skydiver, the safest option might be to get people out, because landing a plane with an engine failure is easier with a light load. This of course depends on altitude, and maybe surrounding options or landing a parachute (forests, mountains or relatively deep water would be bad).
I have done this once, when one of the engines of a twin otter went out at 9000 feet. This is also the reason why skydivers are ALWAYS required to wear their gear fully fastened while in the aircraft. In an emergency, even trained skydivers might not have time, space or stability enough to put on gear properly.
And by gear i mean the parachute, and it's straps. Not necessarily the helmet etc.
For untrained, and/or people not already wearing the harness, I would assume that it is safer to try to land with the aircraft, If in a situation where getting out is at all possible.

Apparently there's also the theoretical possibility of a departing skydiver fatally damaging or entangling the aircraft.  Jumpship pilots usually have parachutes themselves, which would be a bit odd for someone flying any other sort of passengers.

I am doing basic pilot training with the RAF. In our single-engine trainers, we wear and are taught to use parachutes. There is no ejection systems, we have to remove the canopy manually. I don't know why this isn't a standard procedure in all light aircraft, we are doing fairly similar stuff to civilian aviation.
It's nice to know that you have a last resort if the engine is on fire. They aren't a huge amount of use below 1500ft however.

Perhaps because most civilian pilots have a very small chance of being shot down?

It's nothing to do with getting shot down, planes at that risk have ejection seats.

Because small GA aircraft like primary trainers don't have "canopies"? I can barely get out of my C152 when it's stationary on the ground. I couldn't imagine getting out while it's hurtling towards the ground.

Fair point... In which case that would make sense as our trainers do have canopies. Grob Tutor 115E http://en.wikipedia.org/wiki/Grob_G_115

Perhaps the point of your parachute use and training is more about preparation for future need in higher performance, less forgiving aircraft in more hazardous conditions. I think civil aviation doctrine is that the aircraft should never need to be bailed out of... should never exceed its structural limitations, should never get into an unrecoverable flight condition e.g. flat spin, should never run into another aircraft, should never catch on fire, and landing the plane is safer than bailing out of it.

If your RAF trainer is anything like mine was, it's designed explicitly to need the pilot to be wearing a parachute, and it would be more trouble not to wear one.

This may well be to do with the fact that military trainers and the way that they are used are inherently a bit more dangerous than normal civilian light aircraft combined with the fact that military infrastructural and discipline makes obligatory parachute wearing easier to enforce. It may also be a simple training discipline thing to give you an extra (but trivial) thing to check before flight. a bit like polishing your boots and making your bed in a prescribed way during basic training.

The only time I can think of would be if you are flying over a large expanse of unpopulated mountain area.
You are responsible for the damage your plane creates when it impacts with the ground, so there is no time over populated land where there is any control over the aircraft that it is appropriate to bail out of the aircraft and leave the plane flying out of control until impact.
In the mountains where there is no traffic for miles bailing out might give you a better opportunity to be rescued.  A parachute can be controlled and you can put yourself in a better position to survive until rescue.  In the mountains it is much harder to land safely than an area where there are open fields or flat spaces.
Over open water bailing out of the plane might give you a chance to spot and/or be spotted by nearby sailing vessels.  Though if you have some control over your aircraft then you would be better served using that control to ditch in a controlled fashion in visual range of a sailing craft than jumping from the craft.

If the aircraft is uncontrollable anyway staying in if you have a chance of chuting does not make sense damage-wise. Over sparsely populated areas it is quite difficult to hit something relevant at all, be they mountaineous or flat.

If the aircraft is uncontrollable unless you have some sort of automatic ejection seat your chances of getting out in the first place are pretty low.  This question really focuses "Why do pilots often try to find a road to land on or a lake to ditch in when trouble strikes instead of just bringing a parachute and bailing out?"  This sort of infers at least some control.

Agreed - jumping out as long as a survivable landing is still a viable option would be quite debatable.

@yankeekilo - The other issue is there are very few land spaces left on the planet that are truly unpopulated and not a sanctuary or reserve.  If you bail out above 500 feet your plane could go for miles leaving you with no ability to direct where it impacts.  If you bailout below 500 the landing is liable to be painful.

If 100 people parachute in a mountainous region, that will cause a very bad day for the rescue team, as everyone will land at different places. This is considering that most of the passengers will be too untrained and too unorganized to control where they should land.

@LieRyan - This question was scoped to small aircraft - there's often only 1 or 2 passengers (rather than 100).  - not the commercial aircraft.  I would agree though that in a commercial situation so long as the is some control the group is better off trying to survive a landing

@Chad Define 'truly unpopulated.' In the U.S., your chances of hitting anything other than a field or a forest are quite low unless you happen to be in or near a large city. These chances are even lower in, say, Russia, Canada, or Australia. Take a look at the sectional charts in the central or Western part of the U.S. The following are actual landmarks marked on Kansas sectionals: 'elevator' (referring grain elevators... the most common landmark on the Kansas sectionals,) 'stockyard', 'ranch', 'school', 'buildings' (yes, really,) 'church'. You'd have to try to hit something out there.

@Reirab - But unless you are in the mountains there is a real risk that it will impact somewhere that is populated because over most of the country you can draw a 5 mile circle and there is probably at least one if not more human built structure in that area.  In addition if you let the plane go and it causes a forest or wild fire you are responsible for that as well since you abandoned.

Also, airplanes are expensive.  Unless the aircraft is uncontrollable (in which case, as @Chad points out, you'd be very lucky to be able to leave the aircraft anyway), you have a very good chance of being able to land the plane in one piece without major damage.  Bailing out of the aircraft guarantees (okay, almost guarantees) that the aircraft will crash, and have to be written off.

I am a glider and motorglider pilot from Germany. At ours, it's mandatory to have a parachute in gliders (and there was actually one guy i knew who successfully bailed from his glider once due to airframe failure). The glider seats are built with a parachute-wearing pilot in mind. So you can't even sit comfortably in our gliders without a parachute on your back.
In motorized gliders (also in TMGs) it is reccomended to wear a parachute but it's not mandatory. Some pilots do it, others don't.
In the unlikely event of hard-incidents, as we call them, (so: airframe failure, engine fire, permanently blocked sight, for example from bird strikes etc., blocked control surfaces) these pilots with parachutes can actually bail.

I believe most accidents occur during takeoff and landing when the machine and human pilots are most busy.
Unless the aircraft experienced catastrophic failure I think most pilots would prefer to glide the plane down for a rough albeit survivable landing.

Some small aircraft come equipped with ballistic parachute...this is a great idea... :)

In Germany ballistic safety systems are mandatory for aerodynamically controlled ultralights.


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What is an Inertial Navigation System? How does it work?
In this question, the answer notes that some ADS-B systems are connected to Inertial Navigation Systems (INS), and says they are less accurate than GPS.  What exactly is an INS?
A couple sub questions:

Why is it less accurate?
The other post mentions they tend to
develop biases as they get older, why is that?
Are they being phased
out?  Or are they used as backup?

Did you read this? http://en.wikipedia.org/wiki/Inertial_navigation_system What is an INS isn't really something for SE.

@AsheeshR - lol, "welcome to the internet Jay" eh?  No I forgot about Wikipedia in my mad dash to post a question.  The article does answer the first few points quite well, but not the last one.  Plus, I'd like to hear an answer from an aviation expert.  All the same, thanks for the link, that did help my understanding quite a bit.

INS is just plain weird.  It knows where it is by knowing where it started and where it isn't right now.

Inertial Navigation Systems, unlike other navigation systems, do not depend on external (radio) measurements. Instead an INS keeps track of its position by accurately measuring acceleration (accelerometers) and rotation (gyroscopes). It therefore works in remote areas where there are no ground based navaids available.
Initially, the INS gets its position from pilot input at the gate, or in more recent systems from GPS, sometimes even during flight. By measuring all the accelerations and rotations and integrating them into speed and direction the position is tracked. In doing this, the INS has to correct for the rotation of the earth and the related Coriolis force.
Due to small inaccuracies in the measurements the velocity error and, with that, the position errors grow over time.
Wikipedia has quite a detailed article about the history and working of the INS.
While raw INS position has mainly been replaced by GPS measurements on oceanic flights, the system is not being phased out. GPS is a sensitive systems and by crosschecking it with INS, errors can be detected in both systems. It is often used as a backup to GPS.
Integrated GPS / INS systems provide better systems integrity and allow the navigation system to coast through short GPS outages with high accuracies. In addition to that, the (laser) gyroscopes of the INS are often used to provide data to the digital artificial horizon displays in the cockpit and to the auto flight systems. In this case the term Inertial Reference Unit (IRU) is used, which acts as a basis for the INS.

While he didn't ask this, what is the difference between an INS and an IRS?  I hear the terms used almost interchangeably.

@Lnafziger The INS is the term used for the traditional systems based on gimballed gyroscopes designed specifically for navigation. IRS is the term used for modern systems based on laser gyroscopes. The IRS at the heart of the Inertial Reference Unit which does the same as the INS but also provides data to the artifical horizon and autoflight systems. On Airbus and Boeing aircraft it's now integrated with the Air Data Computer and called the ADIRU.

Inertial Navigation System it uses a planes motion as detected by on-board accelerometers and gyroscopes to find where it is going using no external reference points.
A plane has a certain known heading and speed, when the planes makes a turn, hits a headwind,... accelerometers and gyroscopes will detect the change in motion and orientation and update accordingly. This means that initial accuracy depends on the how accurate the initial position speed and heading are when INS is initialized. The accelerometers and gyroscopes have limited granularity/accuracy and extrapolating your position from relative angle changes will compound an earlier error immensely.
For example if the System is off by 1 degree on a turn then after 500 miles it will be off by (500*crd(1°)=500*2*sin(0.5°)=) 8.7 miles assuming all other information is correct. (this example is not fully correct as the gyros measure rate of turn rather than actual angle turned)
INS is used primarily as a supplemental source of navigation data and as a fall back when other sources are unavailable.


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Where does the term 'greased landing' come from?
I've heard this term used a few times to describe a really smooth landing (one where you hardly feel a bump).  But where does this term actually come from?  I'm not sure how grease (a lubricant) came to symbolize a low g-load on landing?

I'm not certain on the etymology of the term, but I imagine it has something to do with the smoothness of the landing (analogous to the smoothness of a well-greased bearing or similar moving parts).

Note that there's a common phrase in English "greased lightning".  (Indeed for example there's a pop song by that name - from the famous film "Grease".) (In that case it's about a 50s hot-rod car.)  It's common in English that people take common phrases (example: "Watergate") and slightly change the phrase (example: "Climate-Gate" etc etc) - often making a sort of pun on the original. Note further that the new variation often does not make that much literal sense; it's more just "kind of funny" because (a) it sort of sounds like the well-known phrase and (b) it kind of makes sense.

The literal answer to the question in the title is: "it is a play on the common English phrase 'greased lightning'."  My guess would be that in aviation in fact it does NOT have a really specific, accurately defined, agreed "meaning".  (Some slang terms have perfectly defined, well-agreed meanings -- some do not; they're more just something that someone has yelled out in excitement on a few occasions.)

@JoeBlow Its an interesting theory, if you have any evidence to support it, feel free to put it in an answer and post it.

@JoeBlow Again, you information is interesting, but coincidence and precedence are not actually evidence.  I'm aware of the phrase, I'm aware of the phenomena you speak of but, frankly, I'm not sure how being a writer qualifies you as an etymologist anymore than being a pilot would qualify one as an electrical engineer.  If you can't be bothered to provide evidence, please state you theories as theories, not answers you can "assure" me of.  Though, again, if you have evidence, I would love to see it.

I've always heard this referred to as a "greased landing" or a "greaser", but never a "greaser landing".
My understanding is that it is referring to a landing that was so good that somebody must have greased the entire runway so that you didn't even feel the airplane touch down.  If you've ever tried to pick something up that has been well greased, then you know what they are referring to.  It's very slippery and slides right out of your hands no matter how hard you try.

Changed it to "greased" :), thanks for the explanation.

Isn't the issue with a greased landing ( a landing where the g-forces felt is extremely minimal ) that the plane is very apt to simply take off again, and is hard to stop due to the lift not being completely gone? Contrasted to a full-stall landing, which is the opposite ( a hard, hard felt, and hard on the gear ) landing is one where there is by definition no lift left?

@CGCampbell You can have a greased landing even to a full stall - If it is done at 1/4" above the runway.  Full stall landings don't have to be hard on the gear or the passengers!

@CGCampbell I don't think it's quite accurate to say that there is, by definition, no lift left in a full stall. If you really have exactly zero lift on touchdown in an airplane, something is probably very wrong and you will probably have a bad day. IIRC, aerodynamic stall is the point at which increasing AoA gives less lift, not none at all.

A stall is defined based on the air flow no longer being linear over the wing. You will still get the force of the air hitting the wing at a high angle providing some lift.

A "Greaser" is a landing where you lift the nose up a bit high, the rear wheels smoothly hit the runway and the nose gradually comes down. It feels like a very smooth landing but but it uses a lot of runway, so can be a problem on a short runway. Generally it is not considered a good thing! You are also more likely to contact the runway a fair distance past the landing point.

Welcome to Aviation.SE! The question was about the origin of the term 'greased landing', not about what it means. You can update your answer with the edit link.


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Could a plane land vertically in a strong headwind?
I know there are VTOL craft meant to take off and land with a vertical trajectory. But, under the perfect wind conditions, could a normal airplane ever land (safely) with a vertical or nearly vertical trajectory?

I don't have video, so I'll leave this as a comment - my father, Capt. Andy Alsop, landed a Loganair Britten Norman Islander at a ground speed that was slightly backwards. This is because the landing speed is about 52kts and the wind that day in Orkney had increased to nearly 60kts.

Well if it could take off...

Can it? Yes. Safely? No.

Is there anything I can add to my answer for you?

Related answer to related question-- https://aviation.stackexchange.com/questions/65219/is-it-possible-to-fly-backward-if-you-have-really-strong-headwind/65233#65233

Yes.
The way to think about these sort of questions is to ask "does the aircraft know that it's moving in relation to the Earth".  The answer to this is "no".
The only thing that matters, and the only thing that the aircraft cares about is airflow (wind) over the wings.
Ignore all sorts of little side effects and imagine an aircraft needs 70 kph of wind over the wings to generate lift and stay afloat, straight and level.
Now, imagine the aircraft is flying along and you could somehow make the Earth disappear but leave behind gravity and the atmosphere.  What would happen to the plane?  Nothing!  It still has 70 kph of wind over the wings and it keeps flying.
Now put the Earth back.  It still keeps flying.
If the pilot reduces the power to 69 kph ("thrust X"), the force generated by lift pushing the aircraft up is a little less than that generated by gravity pulling the aircraft down and the craft will start to descend.  Eventually, it will land (assuming that you remembered to put the Earth back!).
So two scenarios.  First, one where the air is perfectly still and the thrust from the engine ("thrust Y") is pushing the aircraft forward at 70 kph.  Second, where the wind is blowing at 70 kph and thrust Y is such that the aircraft is stationary with respect to the Earth.  Again, the aircraft does not know, or care, that it is stationary with respect to the Earth, just that it has 70 kph of wind over the wings.
Modify the second scenario slightly so that the wind is now 69 kph. The aircraft moves forward at 1 kph. Again, the aircraft does not know, or care, that it is going fowards with respect to the Earth. The wind over the wings is still 70 kph (speed of wind, 69, plus speed of aircraft 1).
Reduce the thrust to X again and the aircraft will start to descend, and also become stationary.  Eventually, it will land with no forward or backward speed.
In reality, this would be almost impossible since the wind is never of a constant speed from a constant direction so little movements would always be taking place.
I have seen a video, which I can no longer find, of a bi-plane which took off into a strong wind, flew backwards down the runway and landed on a spot before the one it took off from.
This comes very close.  With just a little more wind, a vertical landing would have been possible.

There was a great book on aviation history (forget the name - sorry) where a passenger plane took off into the famously strong winds of Patagonia and made no headway pretty much beyond the end of the runway where it flew until finally running low on fuel and (almost crash) landing.

Need to keep that video link handy. It's the perfect answer for every "fly backward", "take off from a treadmill" type question, ever.

I understand the aerodynamics; the two things I was really after with my question were (a) since fast wind near the ground is usually fairly turbulent (as a result of uneven land contours and man-made structures), if that might interfere with landing at speeds comparable to the wind's speed, and (b) what sort of wind conditions and what sort of plane would such a feat require.

@AJMansfield Well, that's a different question (sort of wind and what plane) but you're right about the turbulence, which is why I said almost impossibe.  The Highlander in the video gets awfully close and with a little more wind, if you're prepared to accept the odd kph plus or minus due to the turbulence, then it would have been vertical.  With a really responsive engine, a very fine throttle control and a pilot with excellent reactions, it should always be doable.

Even closer: https://youtu.be/Y7Jwde4EAVw?t=84

Related - https://aviation.stackexchange.com/questions/65219/is-it-possible-to-fly-backward-if-you-have-really-strong-headwind

Under the perfect wind conditions, could a normal airplane ever land (safely) with a vertical or nearly vertical trajectory?
Yes, watch this video: Alaska Super Cub, 10 foot landing, 10 foot take off. Had the wind been a bit stronger the plane would have landed at a null horizontal speed.

I suppose the question, then, is whether such a maneuver would ever be considered "safe". A headwind at or near the design takeoff/landing speeds would very likely exceed the maximum crosswind components by a fair margin, and so as soon as the airplane tried to turn off the runway, it would be blown over like a leaf.

Even if the aircraft continued to face into the wind the whole time it was at an airstrip, it would need to maintain engine power on the ground sufficient to overcome drag from the wind on the leading edges (a little more than approach RPM given that the flaps would be retracted on touchdown), and let us not forget that while the ground speed may be zero, the wind speed definitely isn't, so anyone attempting to deplane is not going to have a very fun time of it.

great video, @robert werner. In a 40HP J-3 cub it is also possible in a very strong headwind to fly slowly backwards. Not a good idea when close to the ground as the cub has no rear-view mirror ;-)

Here's a video of what could well be the same plane, or a very similar one, landing no apparent wheel roll: https://www.youtube.com/watch?v=7vP13XPMNfc. Sorry, can't figure out the formatting to put the link in a comment properly.


text:
How is an ILS approach conducted when following a heavy aircraft?
I'm following a much heavier aircraft on an ILS approach to a large airport.
Ideally I'd like to stay a bit above the glide path and land late, both to avoid the turbulence and also get off the runway quicker.
Is that actually a good idea, and how would I do that in IMC?

By "IMC" do you mean an approach to minimums?

No.  Instrument Meterological Conditions

@CarloFelicione -- I understand what the acronym means -- I'm talking about the context of the question.  There's a huge difference between breaking out shortly after the FAF and having to shoot all the way down to minimums (esp. if this was a NPA vs a PA, but that's neither here nor there)

@UnrecognizedFallingObject, yes, basically worst case.

Other bodies may advise differently but I will answer for the FAA.
The FAA covers this in their wake turbulence handbook as well as many other scenarios you can look over.

Basically you can fly above the glide slope as you have assumed but you should always take precaution as it cant be known if the leading aircraft is at or above slope.
As in similar situations, separation services may be provided, load permitting.

2.10.5.1 Air Traffic Control Assist
Air traffic controllers are able to provide sepa- ration  distance
  information to  pilots  when workload  permits  and  they  have  radar
  dis- plays in the control tower.  They can provide airspeed
  differential between aircraft and may advise pilots following another
  aircraft when they are overtaking the preceding aircraft.

The document outlines some other methods and is worth a read.

The thinking pilot will also consider surface winds and low level winds which, for example, if a tail wind, could put wake turbulence into play even if the pilot flew above the glide path.  However, in my experience flying into heavy traffic NE US airports, the controllers have always provided adequate horizontal spacing, and then even asked if that was acceptable.

Your concerns are valid and any competent approach controller is going to provide adequate spacing for light aircraft flying an approach.  However if you don't feel comfortable accepting an approach clearance, request additional spacing to minimize wake turbulence hazards.  A good controller will offer additional radar vector or send you to a hold in order to provide acceptable sequencing.

To avoid danger due to wake turbulence by preceding aircraft the so called Wake Turbulence Separation is used by ATCOs.
This takes into consideration the wake turbulence categories of both you and the preceding aircraft by this table:
 (ivao.de)
If a case (eg. light - light) is not on the table normal radar separation (3nm) is used.


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Where can I download the coordinates of navigation fixes/intersections?
Is there an exportable public database that I may get a copy of all navigational fixes and their corresponding GPS coordinates (latitude, longitude)?
p.s. Only US airspace navigation fix information is needed.

It would help if you could elaborate a little. Do you want the database of all the fixes in the U.S. Airspace, or Europe, or worldwide?

NFDC 56 Day NASR Subscription. Search for Fix in the sets. Only for the US.

The closest I can think of would be the Navigraph FMS data, however this is provided in multiple formats. Otherwise you can use Skyvector to look at them graphically.


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Does adding flaps during ground roll perform better in short-field takeoff?
In most POHs, the flap configuration for short-field is usually recommended as partial flaps, for instance 10˚ for C172.
I remember the arguments are that full flaps would reduce the acceleration rate, and in no flaps the airplane would have to accelerate to higher speed to off the ground. In either case, the ground roll distance is longer than the optimal partial-flap configurations.
However, this assumes a fixed flap setting during ground roll. How about let the airplane accelerate to a certain speed (in zero flaps) before adding to full flaps? We could achieve best acceleration as well as best lift-off speed?

Timing this correctly would add more workload on the crew, I guess that's a pretty good reason not to do it.

@JustSid perhaps this feature could be added as an automation, for example in a FBY system (yes I know certification process, risk reduction, reliability, ...)

@JustSid I figure there are some tasks of comparable workload, like deploying spoilers/thrust reverser during landing. However, this is even not recommended for multiple crew.

@skyoasis It would be interesting to find out what military pilots do when taking off of short runways-or those threatened by ground fire. Anything you can do to make your lift off quicker would be better, IMO.

Works well in a Supercub. Have a look at any short takeoff competition on Youtube. Full trottle, lift the tail, at the right moment pull two clicks of flap and lower the tail nearly to the ground.

Another one I read somewhere (I think on this site): put flaps down, full power, pull up, accelerate in ground effects, retract flaps, climb out. Never tried that though.

@skyoasis just a theory, as I know more about the mechanics of planes than about flying them, but this could be a safety concern. Imagine if a pilot tried the maneuver you describe only to suffer a total hydraulic failure after passing V1. The plane can no longer abort the takeoff, and may not be able to clear the runway with flaps at zero, potentially resulting in a crash.

@Timpanus: I think very few of the planes to which this would be relevant even have hydraulic systems (except for brakes).  The 172s I've flown had electrically-operated flaps, while my Cherokee is purely mechanical.

@kevin The maneuver you describe sounds like a soft field takeoff, which you have tried if you are an FAA ASEL pilot.

I found this answer is a good analysis.

13.3 - Obstructed-Field - Skimming versus Wheelbarrowing or Flap-Popping
"Another possible procedure (which is usually not recommended) is to keep the flaps retracted until you are ready to leave the runway. Less flaps means less incidence. A big disadvantage is that “popping” the flaps like this increases your workload at a time when there are lots of other things you should be attending to. Another disadvantage is that you run the risk of extending the flaps past the takeoff position to the landing position, creating lots of drag, which is really not what you want in this situation. If your POH calls for this procedure, go ahead, but be careful. Make sure you have some sort of detent to block inadvertent over-extension."
-- John S. Denker, See How It Flies

Flaps have the dual function of increasing lift and drag. When they are fully extended, the drag greatly outweighs the extra lift. So whilst you might have a slightly shortened takeoff run (though I doubt that there is a significant reduction in a C172), you could very well struggle to clear any obstacles. And not forgetting that the takeoff distance required is defined as the distance to climb to 50ft, climbing out on full flaps could actually increase this distance.
You might be tempted to say you should extend the flaps just in time to rotate, then retract them immediately once airborne. Retracting flaps at such a low speed and altitude is incredibly risky. Plus this is a lot of extra work for the pilot at an already critical phase of flight.
In most aircraft, using the smaller flap setting provides extra lift with only a bit of the drag. Always follow the POH - it's written by the folks who know the aircraft and its performance better than anyone.

Maybe a special setting for takeoff would help. The flaps would be set at 10 degrees, but would automatically retract when the squat switches on the landing gear opened.

@HowardMiller I see where you're coming from, but retracting the flaps right after rotation is not safe. The point of having flaps out for a takeoff is to lower the stalling speed, and thus the takeoff speed required. By retracting the flaps, suddenly the stall speed is raised, when you're already at a very slow speed. Flaps at 10 degrees/1 stage in most GA aircraft still provides enough climb performance and lowers the takeoff distance required, so it is the recommended procedure.

it's just an idea. My personal philosophy in design is to keep it as simple as possible.

Yes. But only partial flaps will help; full flaps are almost always a poor choice for takeoff.
What you describe was the standard operating procedure for the Messerschmitt Me-262s in the JV 44. Due to the low thrust at low speed it had a very long takeoff run, and to operate from short airfields designed for propeller aircraft and hastily repaired after attacks it needed to employ this technique. Note on the picture below the small deflection angle, however: This only worked well when the takeoff run was made with zero flaps and then takeoff flaps (not full flaps!) were added shortly before rotation.
The downside was the risk of an overshoot in case the flaps failed to deploy. If your airfield is long enough, it is certainly safer to set the flaps at the beginning of the takeoff run.

Me-262 two-seater replica taking off (picture source)

This is highly dependent on airplane type. Some airplanes have very effective full flaps and some do not.

@GdD: The biggest dependency is flap deflection angle. A split flap is a poor choice for short takeoffs because of its drag, yet for small deflections even this type of flap helps to shorten the takeoff run. The next dependency is flap type, and I assume that is what you meant by airplane type. Sure, other parameters like aspect ratio and sweep also play their part, but when you look at the same aircraft with and without flaps, the deflection angle determines whether those flaps can be helpful or not. For some types of flaps the helpful range of angles is rather small.

@GdD Full flaps are designed for landing (high lift and high drag) and are almost never helpful for shortening the takeoff run. I overlooked that in the question and edited the answer.

I know, that's why I said it's highly dependent on type.